Enhanced node b and methods for network assisted interference cancellation with reduced signaling

ABSTRACT

Embodiments of an enhanced node B (eNB) and methods for network-assisted interference cancellation with reduced signaling in a 3GPP LTE network are generally described herein. In some embodiments, the number of transmission options is reduced by introducing a smaller signaling codebook. In some embodiments, higher-layer feedback from the UE to the eNodeB is established to inform the eNB about certain NA-ICS capabilities of the UE. In some embodiments, the number of signaling options is reduced by providing only certain a priori information. In some embodiments, correlations in the time and/or frequency domain are exploited for reducing the signaling message. In some embodiments, differential information is signaled in the time and/or frequency domain for reducing the signaling message.

PRIORITY CLAIM

This application claims the benefit of priority under 35 USC 119(e) toU.S. Provisional Patent Application Ser. No. 61/843,826, filed Jul. 8,2013 [reference number P59372Z] which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless communications. Some embodiments relateto interference cancellation including network assisted interferencecancellation in 3GPP-LTE networks.

BACKGROUND

Inter-cell, as well as intra-cell, co-channel interference mitigation isone of the most critical tasks of the long term evolution (LTE) userequipment (UE) receiver in order to optimize downlink (DL) throughputand to minimize radio link failures. The type of interference a UEexperiences may vary from Physical Resource Block (PRB) to PRB as wellas from Transmission Time Interval (TTI) to TTI. Furthermore, the typeof interference experienced by a UE depends on the type of allocationsthat UEs in the neighbor cells received from their serving enhanced nodeB (eNB). Conventional interference mitigation techniques do notefficiently address these types of interference.

Thus, there are general needs for improved interference mitigationtechniques in an LTE network. There are general needs for more efficientinterference mitigation techniques in an LTE network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a portion of an end-to-end network architecture of an LTE(long term evolution) network with various components of the network inaccordance with embodiments;

FIG. 2 illustrates interference variance from PRB-to-PRB as well as fromTTI-to-TTI, in accordance with some embodiments.

FIG. 3 shows a structure for the downlink resource grid for downlinktransmissions from an eNB to a UE in accordance with some embodiments;and

FIG. 4 illustrates a functional block diagram of a UE in accordance withsome embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 shows a portion of an end-to-end network architecture of a LTEnetwork with various components of the network in accordance withembodiments. The network comprises a radio access network (e.g., asdepicted, the E-UTRAN or evolved universal terrestrial radio accessnetwork) 102 and the core network (EPC) 120 coupled together through anS1 interface 115. (Note that for convenience and brevity sake, only aportion of the core network, as well as the RAN, is shown.

The core (EPC) 120 includes mobility management entity (MME) 122,serving gateway (serving GW) 124, and packet data network gateway (PDNGW) 126. The RAN 102 includes macro base stations (also referred to asmacro eNodeB or eNB) 105, low power (LP) base stations (or LP eNBs) 106,107, and UEs (user equipment or mobile terminals) 110.

The MME is similar in function to the control plane of legacy ServingGPRS Support Nodes (SGSN). It manages mobility aspects in access such asgateway selection and tracking area list management. The serving GW 124terminates the interface toward the RAN, and routes data packets betweenthe RAN and core network. In addition, it may be a local mobility anchorpoint for inter-eNode-B handovers and also may provide an anchor forinter-3GPP mobility. Other responsibilities may include lawfulintercept, charging, and some policy enforcement. The Serving GW and theMME may be implemented in one physical node or separate physical nodes.The PDN GW terminates an SGi interface toward the packet data network(PDN). It routes data packets between the EPC and the external PDN, andmay be a key node for policy enforcement and charging data collection.It may also provide an anchor point for mobility with non-LTE accesses.The external PDN may be any kind of IP network, as well as an IPMultimedia Subsystem (IMS) domain. The PDN GW and the Serving GW may beimplemented in one physical node or separated physical nodes.

The eNode-B (macro and micro) terminates the air interface protocol andis usually (if not always) the first point of contact for a UE 110. Insome embodiments, an eNode-B may fulfill various logical functions forthe RAN including but not limited to RNC (radio network controllerfunctions) such as radio bearer management, uplink and downlink dynamicradio resource management and data packet scheduling, and mobilitymanagement.

The S1 interface is the interface that separates the RAN and the EPC. Itis split into two parts: the S1-U, which carries traffic data betweenthe eNode-B and the Serving GW, and the S1-MME, which is a signalinginterface between the eNode-B and the MME. The X2 interface is theinterface between eNode-Bs (at least between most, as will be addressedbelow regarding micro eNBs). The X2 interface comprises two parts, theX2-C and X2-U. The X2-C is the control plane interface between eNode-Bs,while the X2-U is the user plane interface between eNode-Bs.

With cellular networks, LP cells are typically used to extend coverageto indoor areas where outdoor signals do not reach well, or to addnetwork capacity in areas with very dense phone usage, such as trainstations. As used herein, the term low power (LP) eNB refers to anysuitable relatively low power eNode-B for implementing a narrower cell(narrower than a macro cell) such as a femtocell, a picocell, or a microcell. Femtocell eNBs are typically provided by a mobile network operatorto its residential or enterprise customers. A femtocell is typically thesize of a residential gateway or smaller and generally connects to theuser's broadband line. Once plugged in, the femtocell connects to themobile operator's mobile network and provides extra coverage in a rangeof typically 30 to 50 meters for residential femtocells. Thus, LP eNB107 may be a femtocell eNB since it is coupled through the PDN GW 126.Similarly, a picocell is a wireless communication system typicallycovering a small area, such as in-building (offices, shopping malls,train stations, etc.), or more recently in-aircraft. A picocell eNB cangenerally connect through the X2 link to another eNB such as a macro eNBthrough its base station controller (BSC) functionality. Thus, LP eNB106 may be implemented with a picocell eNB since it is coupled to amacro eNB via an X2 interface. Picocell eNBs or other LP eNBs for thatmatter) may incorporate some or all functionality of a macro eNB. Insome cases, this may be referred to as an access point base station orenterprise femtocell.

In accordance with embodiments, the eNBs may be arranged for providingnetwork-assistance (NA) interference cancellation signaling (ICS)(NA-ICS) to UEs 110 for coordination of interference mitigation,interference cancellation (IC) or for performing interferencesuppression (IS). In some embodiments, the number of transmissionoptions is reduced by introducing a smaller signaling codebook. In someembodiments, higher-layer feedback from the UE to the eNodeB isestablished to inform the eNB about certain NA-ICS capabilities of theUE. In some embodiments, the number of signaling options is reduced byproviding only certain a priori information. In some embodiments,correlations in the time and/or frequency domain are exploited forreducing the signaling message. In some embodiments, differentialinformation is signaled in the time and/or frequency domain for reducingthe NA-ICS message. These embodiments are discussed in more detailbelow. In some embodiments, an eNB may include physical layer circuitryand processing circuitry for providing network assistance to UEs 110 forcoordination of interference mitigation as discussed herein.

FIG. 2 illustrates how the type of interference varies from PRB-to-PRBas well as from TTI-to-TTI, in accordance with some embodiments. Asmentioned above, inter-cell, as well as intra-cell, co-channelinterference mitigation is one of the more critical tasks of a UEreceiver in order to optimize downlink (DL) throughput and to minimizeradio link failures. When optimizing UE receiver performance or whentrading off performance against UE receiver power consumption and/or UEcost, mitigation of co-channel interference will benefit from networkassistance. In these embodiments, the LTE network may provide sideinformation or coordination or both in combination in order to simplify,enable, or optimize interference cancellation (IC) or interferencesuppression (IS) in the UE receiver. The network assistance informationmay be referred to as “IC/IS side info”, and the (1) Modulation orderand (2) Pre-coder info (e.g., codebook, #TX, Mayers, PMI) of aninterfering signal may be part of the IC/IS side information to beprovided to a UE. For instance: with such IC/IS side info, a (near)maximum likelihood detector in the UE which detects resource blocks 202(FIG. 2) will (ideally) be capable of also demodulating the interfering(UE allocation's RBs 204) signal which is falling in the allocatedresource blocks of the desired UE enabling an ideally completeelimination of the UE allocation's signal (RBs 204) improving DLthroughput of the UE in the serving cell 201. With respect to theinter-cell co-channel interference case in all deployment scenarios andin particular in the homogeneous macro network, appropriate/efficientmethod(s) for signaling IC/IS side information to the LTE UE for thegeneral inter-cell co-channel interference case may need to beaddressed: in particular methods meeting the signaling requirements,minimizing changes to the LTE standard and/or UE receiverimplementation, and optimizing network assistance.

Some embodiments disclosed herein address minimization of the amount ofIC/IS side information and in some embodiments, minimizing the amount ofresources required for providing network assistance information.Embodiments disclosed herein provide several methods to reduce theamount of side-information that has to be signaled for anetwork-assisted interference cancellation and/or suppression receiver.The minimization of signaling is not just an optimization of a potentialNA-ICS scheme but may be considered a requirement given the very limitedavailable signaling bandwidth and the vast amount of interferingtransmission schemes that may be used and would have to be signaled. Ina naïve implementation, the entire information that is sent via PDCCHwould need to be also made available to the interfered UE.

In accordance with embodiments, a signaling method to minimize NA-ICSside information is provided. Depending on the kind of signaling methodused, either the serving eNB or each interfering eNB might signal theNA-ICS side information to the UE.

In the first part of this section, an overview of the possibletransmission options in LTE and explain why the signaling overheadshould be minimized. The second part discloses several embodiments whichmay achieve a significant signaling reduction.

Possible Transmission Configurations Per Interfering Signal:

Depending on the transmission mode in the interfering cell and itsconfiguration, the effective channel may be estimated directly fromprecoded demodulation reference symbols or has to be computed from anestimate of the interfering channel (derived from cell-specificreference symbols) and the precoding that has to be explicitly signaled.In any case, the modulation alphabet (i.e., QPSK, 16QAM, or 64QAM) of asingle transport block or the modulation scheme pair for two transportblocks has to be signaled explicitly. The number of transmit antennaports (as applicable to transmission modes 1-6) used by an interferer aswell as the cell id may be derived by the UE or is signaled (semi)statically.

The following table (Table 1) provides overview per transmission modeused by the interfering cell. In the last column of the table, thenumber of possible configuration options is listed. The numbers areprimarily meant to illustrate the range of possible configurationoptions rather than the exact number as for some transmissions modesthis depends on further assumptions.

TABLE 1 Overview of Transmission Modes and IC/IS Signaling RequirementsNumber of TM Description of Transmission Mode Combinations to considerOptions TM 1 For this single antenna transmission Need to signal 3different 3 mode, no precoding is applied, so modulations. only themodulation alphabet needs to be signaled. Channel estimation isperformed using the cell-specific reference signals (CRS). TM 2/ For theSFBC transmit diversity Need to signal 3 different 3 SFBC schemeconfigured by TM2 and modulations. available as fallback in othertransmission modes, the UE needs to know whether 2 or 4 Tx antennas areused (already signaled or determined in advance, see above) and onlyrequires explicit signaling of the used modulation scheme. Channelestimation is performed using the CRS. TM 3 For the CDD open-loopspatial Rank 1: 30 multiplexing MIMO mode, the 3 different modulationsprecoder deterministically depends on Rank 2-4: the number of Txantennas, the rank, 3 × 3 modulation combinations and the subcarrier/REnumber (see for two different transport 3GPP TS 36.211, 6.3.4.2.2).Besides the modulation scheme, the transmission rank has to be signaled(DCI Format 2A). Channel estimation is performed using the CRS. blocks,i.e. 3 × 3 × 3 = 27 Note: Which of the 16 possible open loop CDDprecoder elements (W(i) * D(i) * U) has been used for the start resourceelement (RE) within a Physical Resource Block (PRB) depends on theposition of the PRB within the interfering UE's TB allocation as well ason the amount of REs unusable for PDSCH to RE mapping. The open-loop CDDprecoder element may be blindly detected on the start RE. TM 4 For theclosed-loop spatial 2 Tx antenna case is a subset of 480 multiplexingtransmission, the 4 antenna case. precoder is selected from a predefinedRank 1: codebook (see 3GPP TS 36.211, 16 PMIs × 3 modulations: 486.3.4.2.3) where the Rank 2-4: precoding matrix depends on the 16 PMIsper rank, 3 × 3 precoding matrix indicator (PMI) and modulationcombinations, 3 the rank. For 2 Tx antennas and different ranks: ranksup to 2, 6 = 4 + 2 different 16 × 3 × 3 × 3 = 432 precoders areavailable and for 4 Tx antennas and ranks up to 4, 64 = 16 × 4 areavailable and have to be signaled. In addition to that, the modulationscheme needs to be signaled. Channel estimation is performed using theCRS. TM 5 This is the MU-MIMO transmission Only rank 1 transmissions: 1648 mode introduced in Rel-8. It supports PMIS times 3 modulations rank-1transmissions per user with 4 or 16 different precoding vectors from theTM4 codebook as indicated by the PMIs. It is still necessary todistinguish TM5 from TM4 though because usually a −3 dB power offset isapplied to each transmission to split the available Tx power between thetwo simultaneously served users. In addition to that, the modulationscheme needs to be signaled. Channel estimation is performed using theCRS. TM 6 This transmission is a subset of TM4 Included in TM4 0restricted to a single layer (i.e., rank 1). For the interfered UE itappears as a rank 1 TM4 transmission so that no special IC/IS signalingis needed. TM 7 This TM allows non-codebook based Not feasible tosupport for NA- 0 precoding transmitting only a single ICS stream.Reference signals are derived from user-specific sequence (C-RNTIdependent, see 6.10.3.1 in 36.211) which cannot be used by theinterfered NA IC/IS receiver to estimate the effective channel unlessthe RNTI would also be signaled. TM 8, These transmission modes rely onExplicit signaling: 237 9, 10 UE-specific precoded demodulationCombinations of 1-2 layers reference signals (DM-RS) which thesupporting MU-MIMO: interfered NA IC/IS receiver can use Ports 7 and 8to estimate the effective channels with scrambling 0 and 1: directly.Thus, only the modulation 3 × 3 × 3 × 3: 4 MU-MIMO layers scheme and thenumber of layers 2 × 3 × 3 × 3: 3 MU-MIMO layers, (2 have to be signaledto the UE choices for scrambling config) together with some scrambling 4× 3 × 3: 2 MU-MIMO layers, (4 related info as described in Table choicesfor scrambling) 5.3.3.1.5C-1 in 36.212. 3 × 3: 1 user, 2 layers 3: 1user, 1 In case of TM 10, DMRS scrambling layer may be initialized withdifferent Virtual More than 3 layers Cell IDs in order to enable thePorts 7-9: 3 × 3 modulations creation of Physical Cell ID- Ports 7-10: 3× 3 modulations independent “areas” for CoMP. The transmission points(TPs) in certain areas may be limited - say e.g. to a set of a fewVCIDs - such that the set of VCID values may Ports 7-11: 3 × 3modulations 12 be communicated as higher layer Ports 7-12: 3 × 3modulations network assistance information. Ports 7-13: 3 × 3modulations Ports 7-14: 3 × 3 modulations Signaling that aids the DM- RSbased modulation signaling with (see other ID): (e.g.) Number of layerspresent Scrambling ID 1

SFBC transmission is available as fallback in almost all othertransmission modes. Embodiments disclosed herein do not need todifferentiate between fallback/non-fallback operations in othertransmission modes because a SFBC/TM2 may be signaled to indicatefallback operation.

From the above overview, for an LTE Rel-11 system about 800 differenttransmission options would need to be distinguished for signaling NA-ICSside info to a UE. A suitable message would thus need 10 bits and wouldonly be valid for the transmissions from one eNodeB on one PRB and TTI.A single eNodeB would thus have to provide up to 100×10=10 kBit ofsignaling information for transmissions on 100 PRBs (20 MHz systembandwidth) per 1 ms TTI leading to a signaling data rate of 10 Mbit/s. ANA-ICS capable UE might want to suppress multiple interfering eNodeBs sothat the required signaling rates would scale further. Clearly, suchhigh signaling rates would be prohibitive or at least severely limit thepotential performance gains.

Methods for Minimizing the Amount of Required Signaling Information:

The basis for the following methods is the existence of a mastercodebook that includes all potential interfering transmissionconfigurations as exemplified in the table above (and potentially more).

Method A: Reducing the Number of Transmission Options by Introducing aSmaller Signaling Codebook:

While there is a huge amount of different transmission possibilities inLTE, only a subset of them will be used in an actual system. Thismotivates restricting the amount of information that is exchanged on aper-TTI basis to the subset of possibilities that is most relevant for alonger period of time (e.g. seconds (thousands of TTIs) or even longer).A master codebook that contains, for example, all of the more than 800transmission options shown in the table above may be provided. Theentries in such a codebook may be encoded with 10 bits or even more. Amuch smaller signaling codebook that allows distinguishing the mostrelevant interfering transmission options from the larger mastercodebook may be provided. Such a codebook could have a size as small as8 (3 bits) or 16 (4 bits) entries and would thus significantly limit theamount of information that has to be signaled on a per TTI basis. Thesignaling codebook may be built semi-statically based on higher layersignaling between the eNodeB and the UE, for example when it registersin the system or initiates high data rate transmissions for which NA-ICSsupport would be beneficial. The higher-layer signaling would requirethe eNodeB to communicate which entries in the smaller signalingcodebook would be filled (i.e. associated) with which entries from themaster codebook. For example, in the case of a 16 entries signalingcodebook, 16*10=160 Bits would be required to signal the completecodebook or 4+10=14 Bits would be sufficient to update a single entry inthe signaling codebook.

With only a few bits necessary to update an entry of the signalingcodebook, the eNB could also adapt the signaling codebook within shortertime frames (e.g., on the order of 50 to 1000 TTIs) to reflect thecurrent scheduling situation. For example, based on the downlink trafficsituation, the eNB serving a user in the interfering cell could predictthat this user will be scheduled during the immediate future and it islikely that only a single or at least only a very limited number oftransmission configurations will be used (e.g., just a singletransmission mode, same number of layers, same modulation scheme, etc.).In that case, this transmission configuration may be added to thesignaling codebook dynamically.

The signaling codebook can also contain a default entry (e.g. 0) whichsimply indicates that none of the previously exchanged options isapplicable so that the UE has to operate without NA-ICS support.

As mentioned above, embodiments disclosed herein are directed toreducing the NA-ICS signaling message. The envisioned signaling codebookmay be built using (higher layer) RRC signaling between a UE and itsserving eNB. The short term per-TTI signaling using this reducedcodebook could then be realized with DCI indication from the serving eNBto the interfered UE. Especially for the short-term signaling, however,different signaling mechanisms that do not rely on an extension of theDCI signaling are feasible. For example, the short-term signaling couldeither be provided by the serving eNB using a non-DCI message, or itcould come from the interfering eNBs directly.

There are many reasons why a much smaller signaling codebook may besufficient to capture the most important out of the many transmissionoptions shown in the table:

-   -   The interfering eNodeBs might have hardware limitations (e.g.        only 2 Tx antennas) that permanently exclude a large amount of        options. For example, all options with ranks>2 would not be        possible.    -   The interfering eNodeBs are configured to operate only with        certain transmission schemes or even do not support them based        on their hardware or firmware implementation.    -   The typical propagation conditions in the interfering cell        could, for example, in the case of a high percentage of        line-of-sight transmissions, make the use of more than, e.g., 2        transmission layers very rare.    -   Some interfering transmission options may be unsuitable        candidates for NA-ICS operation, for example (hypothetically), a        UE might not gain from the knowledge that the interferer has 4        layer transmissions with 64QAM, because such a transmission is        already quite similar to AWGN (AWGN corresponds to an infinite        number of layers or other kinds of transmissions, higher order        modulation also gets closer to AWGN).    -   With the codebook-based precoding (in TM4) the eNodeB can apply        a codebook subset restriction so that certain PMIs will never be        used in the cell.    -   Some of the theoretically feasible transmission options in LTE        may be very rare, for example, operation with CDD open-loop MIMO        in TM3 where the modulation on the two transport blocks is        (very) different.    -   Some LTE transmission modes might never be used in practice        because they are optional (e.g. TM5) or would only be used in a        malfunctioning system (e.g., TM1 with an eNB equipped with two        antennas).

Method B: Establishing Higher-Layer Feedback from the UE to the eNodeBto Inform about Certain NA-ICS Capabilities

The signaling codebook approach mentioned in Method A may be extended byincluding feedback from the UE, i.e., by introducing a hand-shake wherethe UE indicates use cases where NA-ICS would be either very beneficialor not beneficial at all based on the implemented NA-ICS receiver in theUE. This way, the eNodeB can restrict the signaling only to those usecases that are most promising to help the UE receiver. For example(hypothetically), a specific UE receiver implementation might not beable to gain from the knowledge that the interference is modulated with64QAM or that it is using DM-RS based transmission, or it cannot cancelmore than a maximum number of layers.

Method C: Reducing the Number of Signaling Options by Providing OnlyCertain a Priori Information

The UE receiver may be able to blindly detect the presence and structureof certain interfering transmissions. For example, with intra orinter-cell DM-RS based interference, the UE may be able to detect thepresence of interfering layers autonomously and might thus only beinterested in information about the modulation scheme. Or, as anotherexample, the UE receiver may be very powerful and be able toautonomously detect most of the interfering transmission's structure butwould need a prohibitive amount of time or computational resources andpower to do so. To accommodate such cases, some embodiments may augmentthe master codebook of all possible transmission options to include alsoclasses of transmission options that, by signaling those via thesignaling codebook, provide the UE helpful a priori side information. Asan example, the master code book could then contain entries fortransmission Schemes, for example:

SFBC

Codebook-based precoding

CDD open loop precoding

DM-RS based transmission o DM-RS based multiuser

DM-RS based CoMP

Only the modulation of one transport block

The modulation combination of two transport blocks

The provision of side information can, in addition or separately, alsobe done by providing transmission statistics to the UE. For example, ifthe eNodeB semi-statically provides a histogram of how frequentlydifferent transmission modes are used in the cell, the UE can align itsblind-decoding strategy by testing transmission hypotheses in order ofthe signaled likelihood. The histogram information may be provided withmore or less quantization detail (e.g. down to single % or coarse binslike “Top 5%”, “Top 10%”, “Top 35%”, “Rest”). Such statisticalside-information may be provided instead of short-term signaling (thussaving the short term signaling altogether) or as backup information tohelp the UE in blind decoding if a specific transmission option is notcontained in the current signaling codebook.

Method D: Exploiting Correlations in the Time and Frequency Domain forReducing the Signaling Message:

The allocation of interfering transmissions can change per PRB and perTTI as the schedulers in the interfering cells are free to scheduletheir users in the way they want. However, most often there aredependencies in the time and frequency domain because an interferinguser is most often allocated more than 1 PRB, e.g., because depending onthe resource allocation type used, PRBs have to be allocated in resourceblock groups. All PRBs belonging to one user in a considered TTI arerequired by the LTE standard to exhibit the same number of layers andthe same modulation schemes per layer. In addition, the precoding may bedifferent between different PRBs but as the CSI (PMI) feedback uponwhich the eNodeB selects the downlink precoder (in an FDD system) isonly subband specific and thus the same for multiple adjacent PRBs, alsothe precoder for adjacent PRBs will often be identical (in fact, for TM9and TM10 relying on frequency domain PMI/RI reporting, the precoding hasto be identical for groups of adjacent PRBs, see 7.1.6.5 “PRB Bundling”in 36.2 13). In addition, the PRBs for the transmission to one usercannot be distributed in an arbitrary fashion over the frequency range.On the one hand, the downlink control information only allows to signalcertain allocation types (e.g. resource block groups) and, on the otherhand, the CQI feedback can again only be subband specific so that ascheduler would often allocate (groups of) adjacent PRBs.

Thus, the NA-ICS feedback message may be designed to only differentiallyencode the status of adjacent PRBs. One exemplary realization for thesignaling would be to signal for a group of 4 PRBs one entry of thesignaling codebook (e.g. 4 bits) and provide a bitmap for which of the 4PRBs (4 bits) this message is valid. Instead of 4 bits, it may besufficient to only signal 3 bits, because there is little incentive toindicate a configuration that is relevant for no PRB (one case), or fora single PRB only (4 cases), and it is unlikely that it applies to twonon-adjacent PRBs (3 cases: XooX, XoXo, oXoX), leaving 16-1-4−3=8 casesto be signaled with 3 bits. That way, NA-ICS side information may beprovided with 7 (or 8) instead of 16 bits for up to 4 PRBs in thisexample. To enable bigger groups of PRBs where the one NA-ICS signalinginformation is valid for as many PRBs as possible, the eNodeB schedulermay be forced to schedule compatible groups of PRBs accordingly.However, such scheduling restrictions might lead to system-performanceimpairments. Another way

to reduce signaling would be to exploit correlations in the time domainbetween TTIs. This may be done in a similar way as before and could, forexample, also take semi-persistent scheduling (SPS) configurations intoaccount. Finally, the scheduling in neighboring cells may be forced tobe more predictable by the interfered UE so that it would know NA-ICSinformation already in advance. Again, such a limitation of thescheduling in the system is likely to cause major performancedegradation, however.

Method E: Signaling Differential Information in the Time and/orFrequency Domain for Reducing the Signaling Message

This is similar to the previous method, but does not rely on anidentical configuration in adjacent PRBs, but signals differences. Thisis beneficial, if the configurations used for two UEs are similar, whichmay well be the case as the UEs are located in the same cell and maytherefore experience similar channels (at least when located in similarareas of the cell), e.g. similar rank of the channel and thus similarnumber of layers. The configuration of the first UE would be signaled asusual, but for the second UE, only the differences are signaled. In thesimplest (and most general case) the two configurations for the two UEsare signaled, and the division, which PRBs are used for one and theother. The latter information may be signaled using a bitmap typesignaling as mentioned above, but most likely it is sufficient to giveone range (or a couple of ranges) where each UE is scheduled.

FIG. 3 shows a structure for the downlink resource grid for downlinktransmissions from an eNB to a UE in accordance with some embodiments.The depicted grid illustrates a time-frequency grid, called a resourcegrid, which is the physical resource in the downlink in each slot. Sucha time-frequency plane representation is a common practice for OFDMsystems, which makes it intuitive for radio resource allocation. Eachcolumn and each row of the resource grid correspond to one OFDM symboland one OFDM subcarrier, respectively. The duration of the resource gridin the time domain corresponds to one slot in a radio frame. Thesmallest time-frequency unit in a resource grid is denoted as a resourceelement. Each resource grid comprises a number of resource blocks, whichdescribe the mapping of certain physical channels to resource elements.Each resource block comprises a collection of resource elements and inthe frequency domain which represents the smallest quanta of resourcesthat currently may be allocated. There are several different physicaldownlink channels that are conveyed using such resource blocks. Withparticular relevance to this disclosure, two of these physical downlinkchannels are the physical downlink shared channel and the physical downlink control channel.

The physical downlink shared channel (PDSCH) carries user data andhigher-layer signaling to a UE 110 (FIG. 1). The physical downlinkcontrol channel (PDCCH) carries information about the transport formatand resource allocations related to the PDSCH channel, among otherthings. It also informs the UE about the transport format, resourceallocation, and H-ARQ information related to the uplink shared channel.Typically, downlink scheduling (assigning control and shared channelresource blocks to UEs within a cell) is performed at the eNB based onchannel quality information fed back from the UEs to the eNB, and thenthe downlink resource assignment information is sent to a UE on thecontrol channel (PDCCH) used for (assigned to) the UE.

The PDCCH uses CCEs (control channel elements) to convey the controlinformation. Before being mapped to resource elements, the PDCCHcomplex-valued symbols are first organized into quadruplets, which arethen permuted using a sub-block inter-leaver for rate matching. EachPDCCH is transmitted using one or more of these control channel elements(CCEs), where each CCE corresponds to nine sets of four physicalresource elements known as resource element groups (REGs). Four QPSKsymbols are mapped to each REG. The PDCCH may be transmitted using oneor more CCEs, depending on the size of DCI and the channel condition.There may be four or more different PDCCH formats defined in LTE withdifferent numbers of CCEs (e.g., aggregation level, L=1, 2, 4, or 8).

FIG. 4 illustrates a functional block diagram of a UE in accordance withsome embodiments. UE 400 may be suitable for use as UE 110 (FIG. 1). TheUE 400 may include physical layer circuitry 402 for transmitting andreceiving signals to and from eNBs 104 (FIG. 1) using one or moreantennas 401. UE 400 may also include medium access control layer (MAC)circuitry 404 for controlling access to the wireless medium. UE 400 mayalso include processing circuitry 406 and memory 408 arranged to performthe operations described herein. In accordance with embodiments, the UE400 may be arranged to receive network-assistance (NA) interferencecancellation signaling (ICS) (NA-ICS) side information from an eNB forperforming interference mitigation as discussed above.

In some embodiments, the UE 400 may be part of a portable wirelesscommunication device, such as a personal digital assistant (PDA), alaptop or portable computer with wireless communication capability, aweb tablet, a wireless telephone, a smartphone, a wireless headset, apager, an instant messaging device, a digital camera, an access point, atelevision, a medical device (e.g., a heart rate monitor, a bloodpressure monitor, etc.), or other device that may receive and/ortransmit information wirelessly. In some embodiments, the UE 400 mayinclude one or more of a keyboard, a display, a non-volatile memoryport, multiple antennas, a graphics processor, an application processor,speakers, and other mobile device elements. The display may be an LCDscreen including a touch screen.

The one or more antennas 401 utilized by the UE 400 may comprise one ormore directional or omnidirectional antennas, including, for example,dipole antennas, monopole antennas, patch antennas, loop antennas,microstrip antennas or other types of antennas suitable for transmissionof RF signals. In some embodiments, instead of two or more antennas, asingle antenna with multiple apertures may be used. In theseembodiments, each aperture may be considered a separate antenna. In somemultiple-input multiple-output (MIMO) embodiments, the antennas may beeffectively separated to take advantage of spatial diversity and thedifferent channel characteristics that may result between each ofantennas and the antennas of a transmitting station. In some MIMOembodiments, the antennas may be separated by up to 1/10 of a wavelengthor more.

Although the UE 400 is illustrated as having several separate functionalelements, one or more of the functional elements may be combined and maybe implemented by combinations of software-configured elements, such asprocessing elements including digital signal processors (DSPs), and/orother hardware elements. For example, some elements may comprise one ormore microprocessors, DSPs, application specific integrated circuits(ASICs), radio-frequency integrated circuits (RFICs) and combinations ofvarious hardware and logic circuitry for performing at least thefunctions described herein. In some embodiments, the functional elementsmay refer to one or more processes operating on one or more processingelements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage medium, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage medium may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagemedium may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. In these embodiments, oneor more processors may be configured with the instructions to performthe operations described herein.

In some embodiments, the UE 400 may be configured to receive OFDMcommunication signals over a multicarrier communication channel inaccordance with an OFDMA communication technique. The OFDM signals maycomprise a plurality of orthogonal subcarriers. In some broadbandmulticarrier embodiments, eNBs may be part of a broadband wirelessaccess (BWA) network communication network, such as a WorldwideInteroperability for Microwave Access (WiMAX) communication network or a3rd Generation Partnership Project (3GPP) Universal Terrestrial RadioAccess Network (UTRAN) Long-Term-Evolution (LTE) or aLong-Term-Evolution (LTE) communication network, although the scope ofthe invention is not limited in this respect. In these broadbandmulticarrier embodiments, the UE 400 and the eNBs may be configured tocommunicate in accordance with an orthogonal frequency division multipleaccess (OFDMA) technique.

In some LTE embodiments, the basic unit of the wireless resource is thePhysical Resource Block (PRB). The PRB may comprise 12 sub-carriers inthe frequency domain×0.5 ms in the time domain. The PRBs may beallocated in pairs (in the time domain). In these embodiments, the PRBmay comprise a plurality of resource elements (REs). A RE may compriseone sub-carrier×one symbol.

Two types of reference signals may be transmitted by an eNB includingdemodulation reference signals (DM-RS), channel state informationreference signals (CIS-RS) and/or a common reference signal (CRS). TheDM-RS may be used by the UE for data demodulation. The reference signalsmay be transmitted in predetermined PRBs.

In some embodiments, the OFDMA technique may be either a frequencydomain duplexing (FDD) technique that uses different uplink and downlinkspectrum or a time-domain duplexing (TDD) technique that uses the samespectrum for uplink and downlink.

In some other embodiments, the UE 400 and the eNBs may be configured tocommunicate signals that were transmitted using one or more othermodulation techniques such as spread spectrum modulation (e.g., directsequence code division multiple access (DS-CDMA) and/or frequencyhopping code division multiple access (FH-CDMA)), time-divisionmultiplexing (TDM) modulation, and/or frequency-division multiplexing(FDM) modulation, although the scope of the embodiments is not limitedin this respect.

In some LTE embodiments, the UE 400 may calculate several differentfeedback values which may be used to perform channel adaption forclosed-loop spatial multiplexing transmission mode. These feedbackvalues may include a channel-quality indicator (CQI), a rank indicator(RI) and a precoding matrix indicator (PMI). By the CQI, the transmitterselects one of several modulation alphabets and code rate combinations.The RI informs the transmitter about the number of useful transmissionlayers for the current MIMO channel, and the PMI indicates the codebookindex of the precoding matrix (depending on the number of transmitantennas) that is applied at the transmitter. The code rate used by theeNB may be based on the CQI. The PMI may be a vector that is calculatedby the UE and reported to the eNB. In some embodiments, the UE maytransmit a physical uplink control channel (PUCCH) of format 2, 2a or 2bcontaining the CQI/PMI or RI.

In these embodiments, the CQI may be an indication of the downlinkmobile radio channel quality as experienced by the UE 400. The CQIallows the UE 400 to propose to an eNB an optimum modulation scheme andcoding rate to use for a given radio link quality so that the resultingtransport block error rate would not exceed a certain value, such as10%. In some embodiments, the UE may report a wideband CQI value whichrefers to the channel quality of the system bandwidth. The UE may alsoreport a sub-band CQI value per sub-band of a certain number of resourceblocks which may be configured by higher layers. The full set ofsub-bands may cover the system bandwidth. In case of spatialmultiplexing, a CQI per code word may be reported.

In some embodiments, the PMI may indicate an optimum precoding matrix tobe used by the eNB for a given radio condition. The PMI value refers tothe codebook table. The network configures the number of resource blocksthat are represented by a PMI report. In some embodiments, to cover thesystem bandwidth, multiple PMI reports may be provided. PMI reports mayalso be provided for closed loop spatial multiplexing, multi-user MIMOand closed-loop rank 1 precoding MIMO modes.

In some cooperating multipoint (CoMP) embodiments, the network may beconfigured for joint transmissions to a UE in which two or morecooperating/coordinating points, such as remote-radio heads (RRHs)transmit jointly. In these embodiments, the joint transmissions may beMIMO transmissions and the cooperating points are configured to performjoint beamforming.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. A method performed by an enhanced node B (eNB) inan LTE network for providing network assistance to user equipment (UE)for coordination of interference mitigation, the method comprising:indicating a reduced a number of transmission options with a smallersignaling codebook, the smaller signaling codebook having entries thatare a subset of entries of a larger master codebook; and providingnetwork-assistance (NA) interference cancellation signaling (ICS)(NA-ICS) side information to the UE as part of a NA-ICS feedbackmessage, the side information comprising indicators of the smallersignaling codebook, wherein the UE is arranged to perform aninterference cancellation technique based on the smaller signalingcodebook.
 2. The method of claim 1 wherein reducing the number oftransmission options comprises communicating entries of the smallersignaling codebook, the entries of the smaller signaling codebook beingcommunicated with fewer bits than required to communicate entries of thelarger master codebook, wherein the smaller signaling codebook isarranged to capture a predetermined subset of transmission options. 3.The method of claim 2 further comprising: receiving higher-layerfeedback indicating NA-ICS capabilities of the UE; and restrictingtransmission options to the UE based on the NA-ICS capabilities of theUE.
 4. The method of claim 2 further comprising: including entries inthe larger master codebook for predetermined interfering transmissions;and including a subset of the entries for the predetermined interferingtransmissions in the smaller signaling codebook, the subset of theentries being selected based on a likelihood of the UE to experience theinterfering transmissions.
 5. The method of claim 2 further comprising:differentially encoding indicators for groups of adjacent physicalresource blocks (PRBs) as single entries in the smaller signalingcodebook, the groups of adjacent PRBs being identified as interfering.6. The method of claim 5 further comprising signaling differentialinformation in the NA-ICS feedback message with respect to theindicators for groups of adjacent PRBs.
 7. The method of claim 2 furthercomprising: differentially encoding indicators for interferingtransmission-time-intervals (TTIs) as single entries in the smallersignaling codebook.
 8. The method of claim 7 further comprisingsignaling differential information in the NA-ICS feedback message withrespect to the indicators for interfering TTIs.
 9. An enhanced node B(eNB) arranged to provide network assistance to user equipment (UE) forcoordination of interference mitigation, the eNB comprising processingcircuitry arranged to: indicate a reduced a number of transmissionoptions with a smaller signaling codebook, the smaller signalingcodebook having entries that are a subset of entries of a larger mastercodebook; and provide network-assistance (NA) interference cancellationsignaling (ICS) (NA-ICS) side information to the UE as part of a NA-ICSfeedback message, the side information comprising indicators of thesmaller signaling codebook, wherein the UE is arranged to perform aninterference cancellation technique based on the smaller signalingcodebook.
 10. The eNB of claim 9 wherein to indicate a reduced thenumber of transmission options, the eNB is arranged to communicateentries of the smaller signaling codebook, the entries of the smallersignaling codebook being communicated with fewer bits than required tocommunicate entries of the larger master codebook, wherein the smallersignaling codebook is arranged to capture a predetermined subset oftransmission options.
 11. The eNB of claim 10 further configured to:receive higher-layer feedback indicating NA-ICS capabilities of the UE;and restrict transmission options to the UE based on the NA-ICScapabilities of the UE.
 12. The eNB of claim 10 further configured to:include entries in the larger master codebook for predeterminedinterfering transmissions; and include a subset of the entries for thepredetermined interfering transmissions in the smaller signalingcodebook, the subset of the entries being selected based on a likelihoodof the UE to experience the interfering transmissions.
 13. The eNB ofclaim 10 further configured to: differentially encode indicators forgroups of adjacent physical resource blocks (PRBs) as single entries inthe smaller signaling codebook, the groups of adjacent PRBs beingidentified as interfering.
 14. The eNB of claim 13 further configured tosignal differential information in the NA-ICS feedback message withrespect to the indicators for groups of adjacent PRBs.
 15. The eNB ofclaim 10 further configured to differentially encode indicators forinterfering transmission-time-intervals (TTIs) as single entries in thesmaller signaling codebook.
 16. The eNB of claim 15 further configuredto signal differential information in the NA-ICS feedback message withrespect to the indicators for interfering TTIs.
 17. A non-transitorycomputer-readable storage medium that stores instructions for executionby one or more processors to perform operations for providing networkassistance to user equipment (UE) for coordination of interferencemitigation, the operations comprising: indicating a reduced a number oftransmission options with a smaller signaling codebook, the smallersignaling codebook having entries that are a subset of entries of alarger master codebook; and providing network-assistance (NA)interference cancellation signaling (ICS) (NA-ICS) side information tothe UE as part of a NA-ICS feedback message, the side informationcomprising indicators of the smaller signaling codebook, wherein the UEis arranged to perform an interference cancellation technique based onthe smaller signaling codebook.